Studies of both animals and children show that postnatal stress may have lasting effects on brain structure and function, resulting in behavioral and cognitive impairments, particularly for females. It is also unclear how social stress experienced by the mother during gestation synergizes with postnatal stress experienced by her offspring to produce these phenotypes. Importantly, other environmental factors that may interact with stressor exposure to affect brain development during childhood are frequently overlooked, most notably the consumption of calorically dense diets (CDDs) and the resulting metabolic phenotype. Indeed, there is likely a synergy, as chronic social stress is a cumulative risk factor for childhood obesity. Not only may obesity accelerate the tempo of puberty but limited data in children suggest the developing brain is vulnerable to these metabolic insults, as increased body fat is associated with altered brain structure and deficits in cognition and emotional processing. Understanding the impact of stress and obesity on neurodevelopment is critically relevant, given alarming rates of obesity in children, likely due to the consumption of CDDs - a dietary environment quite unlike the typical low caloric diets fed animals used as models for children. Key biological signals could be stress-induced elevations in cortisol and proinflammatory cytokines that are exacerbated by increased fat mass. Prospective studies of the developmental origins of health and disease are difficult to do in children. However, socially housed rhesus monkeys provide an effective translational model, as social subordination produces distinct stress-related phenotypes even during development. This application will address four specific aims to test the overarching hypothesis that prenatal maternal stress interacts with post natal social stress to alter female neurobehavioral development from infancy through puberty and these impairments are exacerbated by obesity. Aim 1 will determine whether increased fat mass interacts with postnatal social stress to alter developmental trajectories of female social and emotional behavior, as well as prefrontal-related cognitive function. Using neuroimaging, Aim 2 will test the hypothesis that social stress and increased fat mass will synergize to alter structural and functional development of the prefrontal cortex (PFC) and its connectivity with regions regulating social and emotional behaviors as well as executive function and self-regulation from infancy, with differences accelerating through the pubertal transition. Mediation analysis in Aim 3 will examine whether cortisol and inflammatory markers mediate the effects of social stress and fat mass on impaired neurobehavioral development. Using cross-fostering, Aim 4 will determine how maternal stress during gestation synergizes with postnatal social stress and obesity to further compromise neurobehavioral development. The project will identify potential biological signals that mediate the adverse effects of stress ad obesity on brain health and behavior and, in doing so, will provide crucial information that will help shape clinical interventions and social policy improvement to optimize neurobehavioral development in girls.